Coordinated signaling of scheduling information for uplink and downlink communications

ABSTRACT

A coordinated signaling scheme for both uplink and downlink transmissions between a base station and a user terminal reduces the amount of time that the user terminal must turn on its receiver to listen for scheduling messages and ACK/NACK signaling. A scheduler at a base station aligns the transmission of downlink scheduling messages (e.g., downlink assignments) with uplink grants and ACK/NACK signaling for uplink transmissions. Aligning the downlink scheduling messages with uplink control signaling enables the user terminal to turn off its receiver for longer periods of time.

RELATED APPLICATIONS

The present application is a continuation of prior U.S. patentapplication Ser. No. 12/609,280, filed 30 Oct. 2009, the disclosure ofwhich is expressly incorporated herein by reference in its entirety.

BACKGROUND

The present invention relates generally to scheduling transmissions toand from user terminals over shared channels in a mobile communicationssystem and, more particularly, to a coordinated signaling schemesupporting both uplink and downlink transmissions over shared channelsdesigned to reduce current drain in a user terminal.

In mobile broadband communication systems, a plurality of user terminalsmay share an uplink and/or downlink channel. For example, the developingstandard for mobile broadband systems known as Long Term Evolution (LTE)provides two shared channels; one for uplink transmissions and one fordownlink transmissions. A scheduler at the base station, referred to inthe LTE standard as an Evolved Node B (eNB), determines which userterminals shall have use of the shared channels at any given schedulinginterval and which resources the user terminals shall use. Schedulingdecisions are typically made once per subframe. Because LTE usesOrthogonal Frequency Division Multiplexing (OFDM), the radio resourcesmay be divided in the frequency domain among two or more user terminalsat any given time.

For downlink communications, the user terminals report channelconditions to the scheduler. The scheduler determines which userterminals to serve based on the reported channel conditions and otherfactors such as buffer levels, quality of service (QoS) requirements,and fairness considerations Data is transmitted to the user terminals onthe Physical Downlink Shared Channel; (PDSCH). The identities of theuser terminals scheduled to receive data in a given subframe aretransmitted to the user terminals in a scheduling message transmitted ona shared downlink control channel, referred to in the LTE standard asthe Physical Downlink Control channel (PDCCH). Thus, the user terminalsmust monitor the PDCCH to determine when they are being scheduled toreceive data on the PDSCH. After receiving data on the PDSCH, the userterminal transmits an acknowledgement (ACK/NACK) to the base station onthe Physical Uplink Control Channel (PUCCH) to indicate whether the datawas successfully decoded. In the case of a NACK, the user terminalcontinues monitoring the PDCCH for scheduling information relating tothe retransmission.

For uplink communications, the LTE standard provides a schedulingrequest mechanism to enable the user terminal to request resources foruplink transmissions. To request resources, the user terminal transmitsa scheduling request (SR) on the PUCCH to the base station, indicatingthat the user terminal has new data to send. The user terminal thenmonitors the PDCCH while it waits for an uplink grant (UL-G). Once theUL-G is received, the user terminal transmits data on the assignedresources Because the SR contains no information about the resourcerequirements of the user terminal, the user terminal attaches a bufferstatus report (BSR) to the first uplink transmission. After transmittingthe data to the base station, the user terminal then monitors thePhysical HARQ Indicator Channel (PHICH) for an ACK/NACK of the uplinktransmission.

The LTE standards supports an operating mode known as discontinuousreception (DRX) to enable the user terminal to conserve power by turningoff some of its radio circuitry. The DRX mode is defined by a DRX cycle,an on-duration, and an inactivity timer. The user terminal wakes up andmonitors the PDCCH at the beginning of every DRX cycle for a periodequal to the on-duration. If no scheduling message directed to the userterminal is received, the user terminal falls asleep until the beginningof the next DRX cycle. When the user terminal receives a schedulingassignment from the base station, it starts the inactivity timer andcontinues to monitor the PDCCH until the timer expires.

While the DRX operating mode is intended to save battery power, theamount of actual savings may be disappointing. The lack of coordinationbetween the uplink and downlink scheduling algorithms may prevent, orsignificantly reduce, potential power savings from DRX operation. Whenthe user terminal is operating in DRX mode, the user terminal may stillneed to turn on its receiver for uplink operations. For example, whenthe user terminal requests resources for uplink transmissions, the userterminal turns on its receiver to monitor the PDCCH while waiting for anuplink grant. Further, HARQ operations for uplink communicationsoverrides DRX operations and the user terminal will turn on its receiverto listen for an ACK/NACK message from the base station. Furthermore,when retransmissions are required for previously-sent downlinktransmissions, the user terminal must turn on its receiver to listen fordownlink scheduling messages.

Because long battery life is a major selling point of mobilecommunication devices, there is much interest in finding ways to reducepower consumption LTE terminals and other future generation userterminals.

BRIEF SUMMARY

The present invention relates to a coordinated signaling scheme for bothuplink and downlink transmissions between a base station and a userterminal that reduces the amount of time that the user terminal mustturn on its receiver to listen for scheduling messages and ACK/NACKsignaling. The basic idea is to align the transmission of downlinkscheduling messages (e.g., downlink assignments) with uplink grants andACK/NACK signaling for uplink transmissions. Aligning the downlinkscheduling messages with uplink control signaling enables the userterminal to turn off its receiver after receiving the downlinkscheduling message. Further, the LTE standard specifies that the uplinktransmission and ACK/NACK signaling for the downlink transmission musttake place four subframes following the uplink grant and downlinkscheduling message, respectively. Thus, the transmitter at the userterminal is turned on at the same time to transmit data on the PUSCH andthe ACK/NACK signaling on the PUCCH. This synchronization enables theuser terminal to turn off its transmitter for longer periods of time.

In some embodiments, the downlink scheduling messages may also bealigned with the ACK/NACK signaling for uplink transmissions. Thisalignment allows the user terminal to turn off its receiver for a longerperiod of time after receiving the downlink scheduling message. Also,aligning the downlink scheduling messages for retransmission with theACK/NACK signaling means that the ACK/NACK signaling for the downlinkretransmission will be aligned with the uplink retransmission. Again,this alignment enables the user terminal to turn off its transmitter forlonger periods of time.

An exemplary embodiment of the invention comprises methods of schedulingtransmissions to a plurality of user terminals over shared uplink anddownlink channels. One exemplary method comprises scheduling downlinkand uplink transmissions for a plurality of user terminals on shareddownlink and uplink traffic channels respectively; transmitting downlinkscheduling messages to said user terminals over a shared downlinkcontrol channel, said downlink scheduling messages indicating theidentities of user terminals scheduled to receive data on the shareddownlink traffic channel in corresponding subframes of a radio frame;and aligning transmissions of uplink scheduling grants for one or moreof said scheduled user terminals with respective downlink schedulingmessages for said scheduled user terminals.

In some embodiments, the method further comprises receiving uplinktransmissions from user terminals scheduled to transmit on said shareduplink traffic channel; scheduling retransmissions to user terminals onsaid shared downlink traffic channel responsive to negative downlinkacknowledgements from said user terminals; and aligning transmissions ofuplink acknowledgements corresponding to transmissions received on saiduplink traffic channel with respective retransmissions to said userterminals on said shared downlink traffic channel.

In some embodiments of the method, scheduling downlink and uplinktransmissions for a plurality of user terminals on shared downlink anduplink traffic channels respectively comprises scheduling downlink anduplink transmissions of voice packets.

In some embodiments, the method further comprises further comprisingappending data packets for user terminals with concurrent voice and datasessions to scheduled voice packets for respective user terminals bytransmitting said data packets for said user terminals with concurrentvoice and data sessions in subframes immediately following thetransmission of respective voice packets.

In some embodiments of the method, scheduling downlink and uplinktransmissions for a plurality of user terminals on shared downlink anduplink traffic channels respectively comprises consolidating downlinktransmissions to said user terminals in one or more subframes of a radioframe to create one or more silent subframes in said radio frame.

In some embodiments, the method further comprises sending a silentsubframe indication to said user terminals to indicate that one or moresubframes of a radio frame will not contain downlink transmissions.

In some embodiments, the method further comprises sending controlsignals to said user terminals to switch user terminals between a normaloperating mode and a power saving operating mode.

In some embodiments, the method further comprises transmittingretransmission window parameters to the user terminals indicating a timeperiod during which downlink retransmissions will be made to the userterminal.

In some embodiments, the method further comprises transmitting randomaccess window parameters to the user terminals indicating a time periodduring which the base station will listen for random access attempts.

Some embodiments of the invention comprise a base station for schedulingtransmissions to a plurality of user terminals over shared uplink anddownlink channels. One exemplary base station comprises a transceiverfor transmitting user data to a plurality of user terminals over ashared downlink traffic channel and for receiving user data from saiduser terminals over a shared uplink traffic channel; a control unitincluding a scheduler for scheduling said downlink and uplinktransmissions. The scheduler is configured to send downlink schedulingmessages to said user terminals over a shared downlink control channel,said downlink scheduling messages indicating the identities of userterminals scheduled to receive data on the shared downlink trafficchannel in corresponding subframes of a radio frame, and to aligntransmissions of uplink scheduling grants for one or more of saidscheduled user terminals with respective downlink scheduling messagesfor said scheduled user terminals.

In some embodiments of the base station, the scheduler is furtherconfigured to schedule retransmissions to user terminals on said shareddownlink traffic channel responsive to receipt of negative downlinkacknowledgements from said user terminals; and to align transmissions ofuplink acknowledgements corresponding to uplink transmissions from saiduser terminals with respective downlink retransmissions to said userterminals on said shared downlink traffic channel.

In some embodiments of the base station, the downlink and uplinktransmissions comprise voice packets.

In some embodiments of the base station, the scheduler is furtherconfigured to append data packets for user terminals with concurrentvoice and data sessions to scheduled voice packets for respective userterminals by scheduling transmission of said data packets fortransmission to said user terminals in subframes immediately followingthe transmission of respective voice packets for said user terminals.

In some embodiments of the base station, the scheduler is furtherconfigured to consolidate downlink transmissions to said user terminalsin one or more subframes of a radio frame to create one or more silentsubframes in said radio frame.

In some embodiments of the base station, the control unit is furtherconfigured to send a silent subframe indication to the user terminals toindicate that one or more subframes of a radio frame will not containdownlink transmissions.

In some embodiments of the base station, the control unit is configuredto send control signals to the user terminals to switch user terminalsbetween a normal operating mode and a power save operating mode.

In some embodiments of the base station, the control unit is configuredto send retransmission window parameters to the user terminalsindicating a time period during which downlink retransmissions will bemade to the user terminal.

In some embodiments of the base station, the control unit is configuredto send random access window parameters to the user terminals indicatinga time period during which the base station will listen for randomaccess attempts.

Other embodiments of the invention comprise methods implemented by auser terminal of receiving downlink retransmission from a base stationover a shared downlink traffic channel. One exemplary user terminalmethod comprises transmitting a negative acknowledgement message to saidbase station to indicate that a previous downlink transmission wasunsuccessful; and intermittently turning a receiver circuit on and offfor a fractional portion of each subframe in a defined retransmissionwindow comprising a plurality of subframes to listen for a downlinkretransmission.

In some embodiments of the user terminal, the method further comprisesturning off the receiver circuit as soon as the decoded control messageis determined to not include a downlink packet assignment for thatsub-frame.

Other embodiments of the invention comprise user terminals for receivingdownlink retransmissions from a base station over a shared downlinktraffic channel. One exemplary user terminal comprises a transceiver forreceiving said downlink transmission and for transmitting control signalon a uplink channel; a control unit configured to transmit a negativeacknowledgement message to said base station to indicate that a previousdownlink transmission was unsuccessful and to intermittently turn areceiver circuit on and off for a fractional portion of each subframe ina defined retransmission window comprising a plurality of subframes tolisten for a downlink retransmission.

In some embodiments of the user terminal, the receiver is furtherconfigured to detect that control message is completed and furtherdetect that a downlink packet will not be sent in that sub-frame, andturn the receiver off.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary mobile communication system for broadcommunications.

FIG. 2 illustrates the structure of an exemplary subframe in mobilecommunication system using OFDM.

FIG. 3 illustrates typical operations for uplink and downlinkcommunications of a base station and user terminal in a mobilecommunication system.

FIG. 4 illustrates typical operations for uplink and downlinkcommunications of a base station and user terminal in a mobilecommunication system according to one embodiment of the invention. Thisexample shows the transmission and retransmission of one uplink and onedownlink voice packet where the retransmission of the downlink packet isaligned with the acknowledgment of the uplink transmission.

FIG. 5 illustrates typical operations for uplink and downlinkcommunications of a base station and user terminal in a mobilecommunication system according to one embodiment of the invention. Thisexample shows the transmission and retransmission of one uplink packetand the transmission of one downlink voice packet.

FIG. 6 illustrates typical operations for uplink and downlinkcommunications of a base station and user terminal in a mobilecommunication system according to another embodiment of the invention.This example shows the transmission and retransmission of one uplink andone downlink voice packet where the retransmission of the downlinkpacket is not aligned with the acknowledgment of the uplinktransmission.

FIG. 7 illustrates typical operations for uplink and downlinkcommunications of a base station and user terminal in a mobilecommunication system according to another embodiment of the invention.This example shows the transmission and retransmission of one uplink andone downlink voice packet along with an appended data packet.

FIG. 8 illustrates an exemplary base station according to the presentinvention.

FIG. 9 illustrates an exemplary user terminal according to the presentinvention.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary wireless communication network 10 forproviding mobile broadband services to one or more user terminals 100.The term user terminal as used herein refers to any portablecommunication device having the ability to connect wirelessly to acommunication network 10. The term user terminal includes, withoutlimitation, cellular phones, smart phones, personal digital assistants,laptop computers, and handheld computers. Wireless communication network10 includes a plurality of base stations 20 that provide radio coveragewithin respective cells 12 of the wireless communication network 10. Thebase station 20 connects to a core network (not shown), which providesaccess to external packet data networks such as the Internet.

For illustrative purposes, an exemplary embodiment of the presentinvention will be described in the context of a Long Term Evolution(LTE) system. Those skilled in the art will appreciate, however, thatthe present invention is more generally applicable to other wirelesscommunication systems, including Wideband Code-Division Multiple Access(WCDMA), WiMax (IEEE 802.16) systems, and future generations of mobilecommunication systems.

LTE systems provides two shared traffic channels; the Physical DownlinkShared Channel (PDCCH) for downlink transmissions and the PhysicalUplink Shared Channel for uplink transmissions. The PDCCH and PUSCH bothuse an orthogonal frequency division multiplexing (OFDM) carrier.Because LTE uses an OFDM carrier, the radio resources may be divided inthe frequency domain among two or more user terminals at any given time.

FIG. 2 illustrates the structure of an exemplary OFDM carrier. Thevertical axis in FIG. 2 represents the frequency domain and thehorizontal axis represents the time domain. In the frequency domain, theradio resource is divided into a plurality of narrowband subcarriers. Atypical OFDM carrier may comprise hundreds or even several thousandsubcarriers. In the time domain, the radio resource is divided into timeslots. Each time slot comprises a plurality of symbol periods. In thisexample, a time slot comprises seven (7) symbol periods. One of thesymbol periods in each time slot is used to transmit a pilot symbol,which is transmitted on a subset of the available subcarriers in a fewknown symbol periods. The remaining six symbols in each time slot areused to transmit data and/or control signals. The subcarriers in a timeslot may be grouped into units known as resource blocks. For example,the exemplary embodiment disclosed herein, a resource block comprisestwelve (12) subcarriers over a period equal to one time slot.

In addition to the shared traffic channels, there are several controlchannels to support uplink and downlink operations. In the downlink, thebase station 20 uses the Physical Downlink Control Channel (PDCCH) totransmit scheduling information and transmission parameters (e.g.,modulation and coding scheme (MCS)) to the user terminals 100 for bothuplink and downlink operations, and the Physical HARQ Indicator Channel(PHICH) for sending acknowledgements of uplink transmissions. In theuplink, the user terminals 100 transmit uplink scheduling requests (SRs)and send acknowledgements (ACK/NACK) of downlink transmissions on thePhysical Uplink Control Channel (PUCCH).

A scheduler at the base station 20 determines which user terminals 100shall have use of the shared traffic channels at any given time.Scheduling decisions are typically made once per subframe. Additionally,the scheduler determines modulation and coding scheme to be used andwhether to use a multiple-input, multiple-output (MIMO) transmissionscheme.

FIG. 3 illustrates typical signaling for downlink and uplinktransmissions on the PDSCH and PUSCH respectively. In the followingexamples, it is assumed that the data transmitted comprises voicepackets for voice over IP (VoIP) service. However, the invention is alsoapplicable to all types of packet data transmissions. These examplesshow the transmission of one speech frame having a period of 20milliseconds (280 bits) over one radio frame, which contains twenty 1millisecond subframes. It is assumed that for normal VoIP operations,one voice frame is being sent every radio frame. The speech frame can becompressed and transmitted in a single OFDM subframe to enable DRXoperation in the downlink.

For downlink communications, the user terminals 100 report channelconditions to the scheduler. The scheduler at the base station 20determines which user terminals 100 to serve based on the reportedchannel conditions and other factors such as buffer levels, quality ofservice (QoS) requirements, and fairness considerations. Data istransmitted to the user terminals 100 on the PDSCH. Once a schedulingdecision is made, the base station 20 transmits voice packets (shown inblack) to the scheduled user terminals 100 on the PDSCH. The identitiesof the user terminals 100 scheduled to receive data in a given subframeare transmitted in a scheduling message called the Downlink Assignment(DL-A) message on the PDCCH. The DL-A message is normally transmitted inthe same subframe as the data transmission. The user terminals 100monitor the PDCCH to determine when they are being scheduled to receivedata on the PDSCH. After receiving data on the PDSCH, the user terminal100 transmits an acknowledgement (ACK/NACK) to the base station 10 onthe PUCCH to indicate whether the data was successfully decoded. The LTEstandard specifies that the ACK/NACK signaling must be sent foursubframes after the downlink transmission. In the case of anunsuccessful transmission, the user terminal 100 sends a NACK on thePUCCH four subframes after the downlink transmission and continuesmonitoring the PDCCH for a new DL-A for the retransmission. Theretransmission from the base station 20 (shown in black) occurs in theninth subframe in this example, which is chosen arbitrarily for thisexample as there is no set time in the LTE standard for theretransmission.

For uplink communications, the user terminal 100 transmits a schedulingrequest (SR) on the PUCCH to the base station 20 when it has data totransmit. The user terminal 100 then monitors the PDCCH while it waitsfor an uplink grant (UL-G). Once the UL-G is received, the user terminal100 transmits voice packets (shown in black) on the assigned resourcesfour subframes following the UL-G. Because the SR contains noinformation about the resource requirements of the user terminal 100,the user terminal 100 attaches a buffer status report (BSR) to the firstuplink transmission. After transmitting the data to the base station 20,the user terminal 100 then monitors the PHICH for an ACK/NACK of theuplink transmission. The LTE standard specifies that the ACK/NACKsignaling should be transmitted four subframes following the uplinktransmission. In the case of an unsuccessful transmission, the userterminal 100 retransmits the data four subframes following the NACK.Those skilled in the art will appreciate that the retransmission maycomprise either the same data originally transmitted, or different dataif incremental redundancy is being used.

FIG. 3 illustrates an example of uncoordinated transmissions on theuplink and downlink. In this example, it is assumed that the eNB isusing a DRX periodicity equal to the speech frame periodicity (20milliseconds in this example) and an inactivity timer of 1 sub-frame.After transmitting the uplink service request (SR), the user terminal100 must turn on its receiver to wait for the uplink grant. The uplinkgrant is received in the sixth subframe. In the example, it is assumedthat the downlink transmission was unsuccessful and that the userterminal 100 thus sends a NACK on the uplink control channel to requesta retransmission. The NACK is sent in the fifth subframe, before theuplink grant is received. Therefore, the user terminal 100 must leaveits receiver on after receiving the uplink grant to listen for a newdownlink scheduling message for the retransmission, which is notreceived until the ninth subframe. In the tenth subframe, the userterminal transmits a voice packet on the uplink. The user terminal 100must turn on its receiver four subframes later, i.e., the fourteenthsubframe, to listen for the ACK/NACK message. In this example, the userterminal 100 is required to turn on its receiver in a minimum offourteen subframes, even if the user terminal 100 is operating in thediscontinuous reception mode. The user terminal 100 also turns on itstransmitter in four subframes out of twenty.

FIG. 4 illustrates an example of coordinated transmissions on the uplinkand downlink in accordance with one embodiment of the present inventionin a scenario where the original uplink and downlink transmissions areunsuccessful. In this example, the base station 20 transmits a downlinkvoice packet in the first subframe. It is presumed that an either uplinkservice request has previously been transmitted to the base station 20by the user terminal 100 on the PUCCH transmitted concurrently with thePUSCH packet from the last speech period. Alternatively, the userterminal 100 could indicate continued uplink voice activity by insertinga Buffer Status Report (BSR) into the PUSCH transmission for the lastspeech frame. Therefore, the base station 20 transmits an UL-G to theuser terminal 100 in the same subframe as the downlink schedulingmessage. According to the LTE Standard, the downlink transmission occursin the same subframe as the transmission of the downlink schedulingmessage. The user terminal 100 is required to transmit an uplink burstin the fourth subframe following the UL-G (i.e., the fifth subframe)Also, the user terminal 100 is required to transmit the ACK/NACK messageon the PUCCH in the fourth subframe following the downlink transmission(i.e., the fifth subframe). Thus, the alignment of the downlinkscheduling message and the UL-G in the first subframe causes theACK/NACK message to be transmitted in the same subframe as the uplinkburst.

It is assumed in this example that the downlink transmission is notsuccessfully decoded and that the user terminal 100 sends a NACK in thefifth subframe. By standard, the base station 20 is required to transmitan ACK/NACK message four subframes following the uplink transmission(i.e., in the ninth subframe). In a preferred embodiment of theinvention, the base station 20 aligns its downlink retransmission withthe ACK/NACK message transmitted to the user terminal 100. Consequently,the downlink scheduling message will be aligned with the ACK/NACKmessage. By standard, the user terminal 100 will acknowledge theretransmission four subframes later (i.e., the thirteenth subframe).Also, because the standard requires the uplink transmission to occurfour subframes after the ACK/NACK message from the base station 20, theuplink retransmission will be aligned with the ACK/NACK signaltransmitted in the thirteenth subframe.

As shown in FIG. 4, the alignment of the downlink scheduling messageswith the uplink grant and ACK/NACK signaling associated with uplinktransmissions means that the user terminal will need to turn on itsreceiver in only slightly more than two subframes in every twentysubframes. In this regard, it may be noted that the receiver needs to beturned on for a short period in the seventeenth subframe to receive thefinal ACK from the base station 20. Similarly, the user terminal willneed to turn on its transmitter in only two subframes out of twenty forthe original transmission and retransmission, respectively Thus,significant power savings can be realized enabling the mobile terminalto turn off its transmitter and receiver for substantially longerperiods of time as compared to the uncoordinated scenario shown in FIG.3. For convenience, the mode of operation shown in FIG. 4 is referred toherein as the power save mode.

FIG. 5 illustrates coordinated transmissions on the uplink and downlinkin the scenario where the downlink transmission is successful so nodownlink retransmission is required. As in the previous example, theoriginal downlink scheduling message and the UL-G are transmitted to theuser terminal 100 in the first subframe. According to the LTE standard,the downlink transmission occurs in the same subframe as thetransmission of the downlink scheduling message. The user terminal 100acknowledges the downlink transmission in the fifth subframe andtransmits the voice packet responsive to the UL-G at the same time.

It is assumed in this example that the downlink transmission issuccessful and that the user terminal 100 sends an ACK in the fifthsubframe. Therefore, there is no retransmission on the downlink. Bystandard, the base station 20 transmits an ACK/NACK message to the userterminal 100 in the ninth subframe (four subframe following the uplinktransmission and the user terminal 100 retransmits in the thirteenthsubframe. Because the ACK/NACK message comprises a single bit, thereceiver does not need to be turned on for the entire subframe. Thus,additional power savings can be realized when no downlink retransmissionis required.

Because the alignment of control signaling for uplink and downlinktransmissions is not currently specified by the standard, the basestation 20 would likely need to send a control signal to the userterminal 100 to switch the operation of the user terminal 100 from anormal mode as specified in the LTE standard to the power save mode. Theuser terminal 100 may indicate that it can operate in a power save modeduring a handshake procedure when the user terminal establishescommunication with the base station 20. The base station 20 may thensend a control signal to the user terminal 100 to direct the userterminal to switch from a normal operating mode as shown in FIG. 3 to apower save mode of operation as shown in FIGS. 4 and 5. This signalingto control whether power save mode is being used or not can occur atvarious times. For instance, it can occur during registration. It canalso occur at call setup, for instance, in the SIP INVITE message usedto initiate the call. Lastly, the user terminal 100 could learn byobservation that the base station 20 was using this invention andautonomously turn on the power save mode based on the assumption that itwill continue for at least the remainder of the call.

FIG. 6 illustrates operations of the user terminal 100 and base station20 in accordance with an alternate embodiment of the invention. In thisexample, the original transmissions of voice packets on the uplink anddownlink are both unsuccessful. In this example, the base station 20transmits a downlink voice packet in the first subframe. It is presumedthat an uplink request has previously been transmitted to the basestation by the user terminal 100. Therefore, the base station 20transmits an uplink grant to the user terminal 100 in the same subframeas the downlink scheduling message. According to the LTE Standard, thedownlink retransmission occurs in the same subframe as the transmissionof the downlink scheduling message. The user terminal 100 is required totransmit an uplink burst in the fourth subframe following the uplinkgrant (i.e., the fifth subframe). Thus, the alignment of the downlinkscheduling message and the uplink grant in the first subframe causes theACK/NACK message to be transmitted in the same subframe as the uplinkburst.

It is assumed that the downlink transmission is not successfully decodedand that the user terminal 100 sends a NACK in the fifth subframe. Bythe standard, the base station 20 is required to transmit an ACK/NACKmessage four frames following the uplink transmission (i.e., in theninth subframe). In contrast to the previous embodiment, the basestation 20 is not required to align the downlink retransmission with theacknowledgement message. Instead, the base station 20 specifies aretransmission window during which the downlink retransmission mayoccur. The retransmission window is defined by two parameters, referredto herein as the offset and the window size. The offset specifies thebeginning subframe of the window relative to the subframe in which theuser terminal 100 transmitted the NACK message. The window sizespecifies the length of the window in subframes. In this example, theoffset is one subframe and the window size is six subframes.

During the retransmission window, the user terminal 100 turns on itsreceiver on and off intermittently to listen for a downlink schedulingmessage. In one embodiment, the receiver is turned on for a fractionalportion of each subframe to listen for the downlink scheduling message.Because the PDCCH is transmitted in the first few symbols of a subframe,the receiver needs to be turned on for only a few symbols in subframeswhere no scheduling message is received. In subframes where a schedulingmessage is received, the receiver is turned on for the entire subframeto receive the downlink transmission. This technique, referred to hereinas microsleeping, allows the user terminal to sleep for short periods oftime during each subframe of the retransmission window. Because thePDCCH can vary from one to three symbols in length depending on theexact circumstances in the network and network control settings, it isadvantageous for the terminal receiver to detect this variation and toturn off as soon as possible after decoding the PDCCH for which there isno downlink packet assigned. The embodiment shown in FIG. 6 has theadvantage of not requiring any additional control signaling other thanthe DRX control signaling already existing in the LTE standard.

FIG. 7 shows an alternate embodiment of the invention for handlingconcurrent voice and data sessions. FIG. 7 illustrates the unsuccessfultransmission of one uplink and one downlink voice packet (shown inblack), and one uplink and one downlink data packet (shown in white). Asin the previous examples, the original downlink scheduling message andthe uplink grant are transmitted to the user terminal 100 in the firstsubframe. The base station 20 transmits a downlink voice packet in thefirst subframe along with an appended data packet in the secondsubframe. The user terminal 100, responsive to the uplink grant,transmits a voice packet to the base station 20 in the fifth subframe.At the same time, the user terminal 100 sends a NACK to the base station20 to indicate that the downlink voice and data packets were notcorrectly received. An appended data packet is transmitted in the sixthsubframe. In this embodiment, the base station 20 aligns the downlinkretransmission with the ACK/NACK of the uplink transmission. The basestation 20 retransmits the voice and data packet in the ninth and tenthframes respectively and sends an acknowledgement of the uplinktransmission at the same time. The user terminal 100 retransmits thevoice and data packet in the thirteenth and fourteenth subframesrespectively and sends an acknowledgement of the downlink retransmissionin the thirteenth subframe.

By transmitting the data packets in the frame immediately following thetransmission of the voice packets, the signaling overhead for datatransmissions can be reduced. This embodiment avoids the need to haveseparate signaling for the data packets. Also, those skilled in the artwill note that a single acknowledgement message is sent for both thevoice and data packets. This may result in the retransmission of somedata that has been successfully received. However, the invention maystill be useful in situations where the system is lightly loaded.

There may be some times when the system is lightly loaded and the basestation does not need all of the available spectrum to provide serviceto the user terminals 100. According to one aspect of the invention, thescheduler can be programmed to consolidate the downlink transmissionsinto the fewest possible number of subframes to create “silent”subframes where there are no downlink transmissions. The base station 20can indicate through signaling the number of subframes being used sothat the user terminal 100 do not need to listen for downlinktransmissions in the silent subframes.

In another aspect of the invention, the base station 20 may limit thesub-frames that it will listen to for RACH attempts. The base station 20could indicate the subframes used for RACH transmissions, referred toherein as the RACH window, on a broadcast system information message.This would allow the base station receiver to be off except during thescheduled times using this invention. Also, we should mention that thebase station 20 could use a similar “micro-sleep” technique to listenonly to the beginning few symbols of each sub-frame of the RAC window.

FIG. 8 illustrates an exemplary base station 20. The base station 20comprises transceiver circuits 22 coupled to an antenna 24 forcommunicating with one or more user terminals 100, and a control circuit26 for controlling the operation of the base station 20 as describedabove. The control circuit 26 may comprise one or more processors thatcarry out the various control functions, such as radio resource control.The control circuit 26 includes a scheduler 28 to schedule uplink anddownlink transmissions as described above. The scheduler 28 isresponsible for determining which user terminals 100 to schedule fortransmission during each subframe and to send a scheduling messages anduplink grants to the scheduled user terminals 100.

FIG. 9 illustrates an exemplary user terminal 100. The user terminal 100comprises a transceiver 110 coupled to one or more antennas 102, abaseband processing circuit 120 for processing signals transmitted andreceived by the user terminal 100, and a control unit 130 to control theoverall operation of the user terminal 100 as described in thisapplication. The baseband processing circuit 120 and control unit 130could be implemented in a one or more programmable processors and/orhardware circuits.

The present invention may, of course, be carried out in other specificways than those herein set forth without departing from the scope andessential characteristics of the invention. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive, and all changes coming within the meaning and equivalencyrange of the appended claims are intended to be embraced therein.

What is claimed is:
 1. A method implemented by a user terminal ofreceiving downlink retransmission from a base station over a shareddownlink traffic channel, said method comprising: transmitting to saidbase station an uplink message and a negative acknowledgement messagewith aligned timing, wherein the uplink message is in response to asuccessfully received uplink scheduling grant and the negativeacknowledgement indicates that a previous downlink transmission from thebase station was unsuccessful; and intermittently turning a receivercircuit on and off for a fractional portion of each subframe in adefined retransmission window comprising a plurality of subframes tolisten for a downlink retransmission.
 2. The method of claim 1, themethod further comprises the user terminal receiving an uplinkscheduling grant in the same subframe as the user terminal receives adownlink scheduling message, wherein said transmitting of the uplinkmessage is in response to a coordinated transmission of the uplinkscheduling grant in dependence on the timing of the downlink schedulingmessage, and wherein the downlink scheduling message indicates that theuser terminal is scheduled to receive data on the shared downlinktraffic channel in corresponding subframes of a radio frame.
 3. Themethod of claim 1, wherein the uplink message and the negativeacknowledgement message are transmitted in aligned subframes on anuplink data channel and an uplink control channel, respectively.
 4. Themethod of claim 1, wherein the fractional portion of each subframe is abeginning portion of each subframe.
 5. The method of claim 1, furthercomprising receiving a scheduling message during the fractional portionof one of the subframes and keeping the receiver circuit turned on for aremainder of the subframe.
 6. The method of claim 1, further comprisingturning the receiver circuit off for each subframe after decoding aPDCCH for which there is no downlink packet assigned.
 7. The method ofclaim 1, further comprising turning off the receiver circuit after adecoded control message is determined to not include a downlink packetassignment for the subframe.
 8. The method of claim 1, furthercomprising turning off the receiver after detecting that a controlmessage is completed and that a downlink packet will not be sent in thesubframe.
 9. The method of claim 1, further comprising indicating to thebase station during a handshake procedure that the user terminal willoperate in a power save mode.
 10. The method of claim 1, wherein thenegative acknowledgement message indicates that a previous downlinktransmission of one or more voice or one or more data packets wasunsuccessful, and wherein intermittently turning a receiver circuit onand off comprises to listen for a downlink retransmission of the one ormore voice and the one or more data packets.
 11. A user terminalconfigured to receive downlink transmission from a base station over ashared downlink traffic channel, said user terminal comprising: atransceiver for receiving said downlink transmission and fortransmitting control signal on an uplink channel; a control circuitconfigured to: transmit to said base station an uplink message and anegative acknowledgement message with aligned timing, wherein the uplinkmessage is in response to a successfully received uplink schedulinggrant and the negative acknowledgement indicates that a previousdownlink transmission from the base station was unsuccessful;intermittently turn a receiver circuit on and off for a fractionalportion of each subframe in a defined retransmission window comprising aplurality of subframes to listen for a downlink retransmission.
 12. Theuser terminal of claim 11, wherein the transceiver is configured toreceive an uplink scheduling grant in the same subframe as a downlinkscheduling message, and wherein the control circuit is configured totransmit the uplink message in response to a coordinated transmission ofthe uplink scheduling grant in dependence on the timing of the downlinkscheduling message, and wherein the downlink scheduling messageindicates that the user terminal is scheduled to receive data on theshared downlink traffic channel in corresponding subframes of a radioframe.
 13. The user terminal of claim 11, wherein the control circuit isconfigured to transmit in aligned subframes the uplink message and thenegative acknowledgement message on an uplink data channel and uplinkcontrol channel, respectively.
 14. The user terminal of claim 11,wherein the fractional portion of each subframe is a beginning portionof each subframe.
 15. The user terminal of claim 11, wherein thetransceiver is configured to receive a scheduling message during thefractional portion of one of the subframes and the control circuit isconfigured to keep the receiver circuit turned on for a remainder of thesubframe.
 16. The user terminal of claim 11, wherein the control circuitis configured to turn the receiver circuit off for each subframe afterdecoding a PDCCH for which there is no downlink packet assigned.
 17. Theuser terminal of claim 11, wherein the control circuit is configured toturn off the receiver circuit after a decoded control message isdetermined to not include a downlink packet assignment for the subframe.18. The user terminal of claim 11, wherein the control circuit isconfigured to turn off the receiver after detecting that a controlmessage is completed and that a downlink packet will not be sent in thesubframe.
 19. The user terminal of claim 11, wherein the user terminalis configured to indicate to the base station during a handshakeprocedure that the user terminal will operate in a power save mode. 20.The user terminal of claim 11, wherein the negative acknowledgementmessage indicates that a previous downlink transmission of one or morevoice or one or more data packets was unsuccessful, and wherein thecontrol circuit is configured to intermittently turn a receiver circuiton and off to listen for a downlink retransmission of the one or morevoice and the one or more data packets.